Water jet drill bit

ABSTRACT

A rock is excavated by the steps of forming at least one groove in the rock by a water jet, forcing a first single-bevel cutter into the rock while the cutter is moved along a line parallel to and spaced apart from the groove so that cracks formed by the cutter and reaching the groove are thereby formed mostly by tensile failure of the rock, further forcing the first cutter through the rock until a succeeding second single-bevel cutter moving along a path further from the groove than the first cutter is forced against the rock so that cracks starting from the second cutter and reaching the groove are thereby formed, and continuing this procedure similarly until all of several sequentially staggered and succeeding cutters act on the rock. The apparatus has an excavation head on which nozzles and cutters are so arranged that the above described method can be put into practice thereby.

Takahashi et al.

[ 1 WATER JET DRILL BIT [75] Inventors: Hikoji Takahashi; Seisuke Misawa;

Akinori Takahashi; Hisashi Yoshimura, all of Tokyo, Japan [73] Assignee: Nippon Kokuyu Tetsudo, Tokyo-to,

Japan [22] Filed: June 11, 1973 [21] Appl. No.: 368,999

[30] Foreign Application Priority Data June 15, 1972 Japan 4769048 (52] US. Cl 175/393, 175/67, 175/397, 299/17, 299/81 [51] Int. Cl E21b 9/35 [58] Field of Search 175/329, 330, 334, 339, 175/340, 377, 391, 393

[56] References Cited UNITED STATES PATENTS 2,662,738 12/1953 Davis et a1. 175/330 3,537,538 11/1970 Generoux 175/330 l 1 1 Re Bai ek PzR' a/ 1 Feb. 11, 1975 Primary ExaminerErnest R. Purser Attorney, Agent, or Firm-Stevens, Davis, Miller & Mosher [57] ABSTRACT A rock is excavated by the steps of forming at least one groove in the rock by a water jet, forcing a first single-bevel cutter into the rock while the cutter is moved along a line parallel to and spaced apart from the groove so that cracks formed by the cutter and reaching the groove are thereby formed mostly by tensile failure of the rock, further forcing the first cutter through the rock until a succeeding second singlebevel cutter moving along a path further from the groove than the first cutter is forced against the rock so that cracks starting from the second cutter and reaching the groove are thereby formed, and continuing this procedure similarly until all of several sequentially staggered and succeeding cutters act on the rock. The apparatus has an excavation headon which nozzles and cutters are so arranged that the above described method can be put into practice thereby.

5 Claims, 15 Drawing Figures PATENTEDFEBI H975 3,865,202

sum 10F 4 F|G.|A FIGJB PATENTEDFEBI 1 I915 3.865202 SHEET 3 BF 4 FIG. 5A

FIG. 5B

PATENTEU FEB] H975 SHEET U 0F 4 WATER JET DRILL BIT BACKGROUND OF THE INVENTION This invention relates to a method for excavating tun- In the case where a tunnel is excavated by the use of an excavator having a rotating cutter head, wear of the cutters has been intolerably great when the hardness of the rock is high and has resulted in elevated excavation cost and reduction of the excavation speed.

For overcoming the above-mentioned disadvantages, there have been proposed various methods including cutting grooves in the rock by means of super-highpressure water jets or weakening the rock by applying a flame jet, laser beam, or microwave radiation onto the rock.

Among these methods, one wherein a plurality of grooves cut in the rock by means of super-highpressure water jets are-utilized in combination with the cutting action of a plurality of cutters provided on a cutter head is found to be advantageous because it requires a far smaller force than others for advancing the cutter head in the excavating direction. The reason for this is that when each of the cutters provided on the cutter head is forced to act on a land portion between adjacent grooves previously formed in the rock by high-pressure water jets, the rock is broken mostly under shearing stress, and the shearing strength ofthe rock is approximately in a range of from one-fifth to 1/10 of the compression strength of the rock.

In such a conventional method, if it is desired to preserve such an advantageous feature of requiring substantially reduced'force for propelling the cutter head forwardly, the number of the grooves must be increased to such an extent that each cutter can be operated between two adjacent grooves so that the rock is crackedunder shearing stress along lines starting from the cutter position to the grooves. In the conventional cutter head, since many cutters are arranged in a single plane parallel to the front surface of the cutter head, the required number of grooves must be great in the case where the above described relative disposition between the cutters and the grooves is to be maintained, and therefore the power required for supplying superhigh-pressure water jets for forming a great number of grooves is extremely high when the area to be excavated is considerably large. This is not only a waste of power but also produces a difficulty in finding a space for the super-high-pressure generating apparatus within the narrow tunnel excavation area or the like.

SUMMARY OF THE INVENTION Thus, a primary object of the present invention is in one aspect thereof to provide an improved excavation method utilizing grooves formed in rock by water jet whereby all of the above described drawbacks of the conventional methods are substantially overcome.

More specifically, an object of the present invention is to provide an improved excavation method utilizing grooves formed in rock by water jet, wherein the number of grooves can be substantially decreased.

Another object of the invention is to provide an improved excavation method utilizing grooves formed in rock by water jet and using a cutter head, wherein the force required for advancing the cutter head is substantially reduced. 4

Still another object of the invention is to provide an improved excavation method utilizing grooves formed in rock by water jet, wherein the rock is broken mostly by tension stress.

Still another object of the invention is to provide an excavation apparatus for practicing the improved method according to the present invention with all of the above described features preserved.

With all of the above described objects and required features in view, the excavation method according to the present invention comprises the steps of forming at least onegroove in a rock or rocky mass by means of a super-high-pressure water jet, forcing a first cutter into the rock at a point on at least one side of and spaced apart from the groove while causing the cutter to travel along a line substantially parallel to the groove thereby to create in the rock cracks running from said line to said groove principally by tensile stresses to remove part of the rock, advancing a second cutter after said first cutter to force it into the rock while causing the second cutter to travel along a line substantially parallel to the groove and more remote from the groove than the first mentioned line thereby to create in the rock cracks running from the second mentioned line to the region of the first mentioned cracks to re move another part of rock, and advancing successively a third and following cutters in similar manner and disposition to remove further rock parts from the at least one side of the groove.

According to the invention, in another aspect thereof, there is provided an improved excavation apparatus whereby the above described excavation method can be put into practice, the apparatus comprising an excavating head adapted to rotate about an axis and having a forward face having at least one annular groove formed coaxially therein means for rotating the head, means for advancing the head with the forward face thereof confronting the rocky ground to be excavated, nozzles for ejecting super-high-pressure water jets provided on the inner and outer peripheries of said groove, and a plurality of cutters disposed in said groove at radially different positions with an arrangement such that they are stepwisely retracted toward the central part of the width of the groove relative to the forward face of the head with respect to the advancing direction of the head.

The invention will be better understood from the following detailed description of the invention with referonce to the accompanying drawings wherein like parts are designated by like reference numerals and characters.

BRIEF DESCRIPTION OF THE DRAWINGS In the drawings:

FIGS. 1A, 1B, and 1C are fragmentary sectional views indicating the principle of breaking rock in a conventional excavation method wherein grooves formed by a super-high-pressure water jet are utilized;

FIG. 2 is a schematic end view showing the forward face of an excavation head in an excavator constituting one part of the present invention;

FIG. 3 is a sectional view-taken along the line III-III in FIG. 2;

FIG. 4 is an enlarged view showing a part of FIG. 3;

FIG. A is a sectional diagram showing a beginning stage of excavating rock;

FIG. 5B is a diagram similar to FIG. 5A, but showing a slightly advanced stage of the excavation;

FIG. 5C is a diagram similar to FIG. 5B, but showing a further advanced stage of the excavation;

FIG. 5D is a diagram similar to FIG. 5C, but showing a still further advanced stage of the excavation;

FIG. SE is a diagram similar to FIG. 5D. but showing a finally obtained excavated condition in which the excavation is continued;

FIG. SP is a diagram showing relative positions of the rock and the cutters during the excavating operation; and

FIGS. 6 through 8 are sectional diagrams showing the principle of excavating rock in accordance with the present invention.

DETAILED DESCRIPTION OF THE INVENTION As conductive to a full understanding of the present invention, the principle of a conventional method of excavating rocky ground by the use of water jet formed grooves is first presented with reference to FIGS. 1A, 1B, and 1C.

In rocky ground R to be excavated, avated, grooves G are formed by a super-high-pressure water jet, and a disc cutter C is caused to travel along the land portion between two adjacent grooves G while a thrust is applied to the cutter C in a direction as designated by an arrow mark. In FIG. 1A, there is indicated a state prior to the start of excavation. When the cutter C starts to be driven into the rock R as shown in FIG. 1B, components of the thrust act in the directions of arrows from the cutter C to the rock R, whereby the rock R is broken along lines 2 running from below the cutter C to the grooves G by tensile stressses. When the cutter C is further driven into the rock R, as shown in FIG. 1C, the rock R is broken along lines 3 running from the cutter C to the edges ofthe groove G. The above described procedure is repeatedly successively so that the excavation through the rock is accomplished.

Referring now to FIGS.-2 and 3, there is shown an ex ample of an excavation head used in an excavator according to the present invention. The excavation head is generally designated by H and comprises a main body 4 of a disc-like configuration. The main body 4 is rotated around its axis X-X by a driving device (not shown).

In the forward surface 5 of the main body 4, there are formed two concentric annular grooves 6 and 7 ofa triangular cross section, and at least one nozzle N for supplying a super-high-pressure water jet is provided on each of the outer peripheral rim of the forward surface 5, an intermediate crest between the grooves 6 and 7, and a central land encircled by the inner groove 6. Super-high-pressure water may be supplied through passages (not shown) in the main body 4 to these nozzles N. Although only one nozzle N for each ofthe outer peripheral rim, intermediate crest, and central land is actually sufficient for accomplishing its function, these nozzles N are shown in FIG. 3 at positions which correspond to intersections of the loci of the movement of the nozzles and a diametrical plane in which the axis X-X lies for purpose of explanation.

Rock Cutters A], A2, A3, A4, A5, and B1, B1, B3, B4, B5 are rigidly secured to the two side walls of the outer groove 7 and are formed with a single bevel cutting edge instead of a double bevel cutting edge of the cutters shown in FIG. 1. Furthermore, the cutters are arranged on the side walls in such a manner that the tips thereof are successively retracted from the forward 5 plane 5 of the main body 4. More specifically, the heights of the tips of the cutters A,, A A A,, and A, measured from the bottom of the groove 7 are selected to be 1,, 1 I 1,, and 1,, as shown in FIG. 4, which are successively decreased in this order. It will be noted that, because of the above described disposition of the cutters A, through A,,, the distances of retraction of the I cutters from the forward plane 5 are greater toward the bottom of the groove 7. The same relation is also applicable to the cutters B, through 8,. In the inner groove 6, cutters C,, C C C and D,, D D D, are provided in a manner similar to that described above with respect to the cutters A, through A, and B, through 8,. As shown, all the cutters may be inclined away from the nearest cutters. In this case, a self-sharpening property is afforded to the cutter, i.e., the tips of the cutters are automatically sharpened or shaped while they are cutting the rock.

In FIG. 3, all of the cutters are shown in a single sectional plane passing through the rotating axis of the ex- 'cavation hard H for the purpose of clarity. However, these cutters are actually distributed along four radii perpendicular to each other as best illustrated in FIG. 2. Furthermore, as is also apparent in FIG. 2, all of the cutters are arranged in such a manner that the cutters in the same groove have different loci, e.g., the locus for the cutter A, is outside of the locus for the cutter B2.

Furthermore, a cone cutter 8 is provided at the center of the forward surface 5 of the main body 4, and the cone cutter 8 acts as a leading cutter which is firstly driven into the face of the rock when the excavation head H is forced in directions of arrow marks T indicated in FIG. 3.

The operation of the excavating apparatus provided with the head as above described will now be described in more detail with respect to an example wherein a tunnel is excavated by the excavating apparatus.

First, the excavating apparatus is placed at a suitable place near the working face of the tunnel, and the excavation head H is rotated in the arrow-marked direction P in FIGS. 2 and 3, with the forward face thereof confronting the rocky face. Simultaneously, super-highpressure water is ejected from the nozzles N toward the rocky face of the tunnel so that, for instance, three annular grooves of several-centimeters depth are formed in the rock. Because of the presence of the annular grooves, the free surface area of the rock R is increased.

When the excavation head H is urged forward, the cone cutter 8 at the center of the excavation head H is forced into the rock R, and then the cutters A, through A B, through 8,, C, through C.,, and D, through D, are successively brought into engagement with the rock, so that the rock is broken by tensile stress.

In FIGS. 6, 7, and 8, there are illustrated different stages of the rock breaking process with respect to the cutters A A.,, and C,, C;,. When the groove G is formed in the rock R by means of a water jet ejected from the nozzle N, and the cutter C, is started to be driven into the rock R, cracks 10 starting from the cutter position and reaching the groove G are thereby created under tensile stress as shown in FIG. 6, and a part R, of the rock R is thereby removed.

With a further advance of the excavation head, the cutter C is further driven into the rock R creating cracks 12 also reaching the groove G in the rock. At the same time, cutters A and C are driven into the rock R successively, whereby cracks 11 are created on the side of the groove G opposite to the cutter C l and cracks 13 are created outside (relative to the groove G) of the cracks 10.

During this operation, the nozzle N is also advanced cutting the groove G far deeper, and when the excavation head is advanced as shown in FIG. 8, the cutters C A and C create further cracks l5, l6, and 17, respectively, while still another cutter A following the cutter C starts to be driven into the rock R, and cracks 14 are thereby formed.

As a result of the above described procedure, the rock R is excavated stepwisely as shown in FIG. 5A through FIG. 55 by the cutters stepwisely disposed on both sides of the groove G, and the relative positions of the thus excavated rock and the cutters are shown in FlG. 5F.

As is apparent from the above description, according to the present invention,'a characteristic property of rock whereby the tensile strength thereof is in a range of approximately from l/lO'to 1/20 of its compression strength is utilized, and the rock is thereby broken mostly by tensile stresses. For this reason, the force required for driving a cutter into the rock can be reduced to approximately from 60% to 80% of that of the conventional procedure. wherein compresssive breaking or shear breaking is utilized, and the numbers of the cutters and grooves required for excavating rocky ground can be substantially reduced. As a result, the excavating speed can be increased by 20 30%-over that of the conventional method, and the cost for replacingor repairing the cutters can be reduced by 30% or more.

We claim: 1. An'appara'tus for excavating a rock comprising an excavating head adapted to rotate about an axis and having a forward face having at least one annular groove formed therein and having a center on said axis, means for rotating the head, means for advancing the head with the forward face thereof confronting the rock, nozzles for ejecting super-high-pressure water jets provided on the inner and outer peripheries of saidgroove, and a plurality of cutters disposed in said groove at radially different positions with an arrange ment such that they are stepwisely retracted relative to the forward face of the head with respect to the advancing direction of the head toward the central part of the width of the groove.

2. An apparatus as set forth in claim 1 wherein said cutters are arranged in the front face of said excavating head-along four radii thereof with spacing therebetween.

3. An apparatus as set forth in claim 1 wherein a cone cutter is provided at the center of the forward face of the excavation head.

4. An apparatus as set forth in claim 1 wherein all of the cutters except the central cone cutter have singlebevel cutting tips.

5. An apparatus as set forth in claim 1 wherein said cutters are inclined relative to a direction parallel to the axis of the excavating head away from the nozzles nearest thereto. 

1. An apparatus for excavating a rock comprising an excavating head adapted to rotate about an axis and having a forward face having at least one annular groove formed therein and having a center on said axis, means for rotating the head, means for advancing the head with the forward face thereof confronting the rock, nozzles for ejecting super-high-pressure water jets provided on the inner and outer peripheries of said groove, and a plurality of cutters disposed in said groove at radially different positions with an arrangement such that they are stepwisely retracted relative to the forward face of the head with respect to the advancing direction of the head toward the central part of the width of the groove.
 2. An apparatus as set forth in claim 1 wherein said cutters are arranged in the front face of said excavating head along four radii thereof with 90* spacing therebetween.
 3. An apparatus as set forth in claim 1 wherein a cone cutter is provided at the center of the forward face of the excavation head.
 4. An apparatus as set forth in claim 1 wherein all of the cutters except the central cone cutter have single-bevel cutting tips.
 5. An apparatus as set forth in claim 1 wherein said cutters are inclined relative to a direction parallel to the axis of the excavating head away from the nozzles nearest thereto. 